If you aren’t already using Evernote, stop reading this and download it immediately. I use it to keep track of everything from blog post ideas, to the color codes for my website, to travel packing lists. It can be as simple or as complex as you’d like, and because it syncs over multiple devices (desktop, phone, and cloud for online access) you’re never far from your notes.
I like Wunderlist for its flexibility and especially for the repeat task feature. I have once-a-week repeating tasks to refill my vitamins, clean my apartment, and check my online accounts. It’s freeing to know that the app will email me reminders
ColorNote (Android only)
Spectacular in its simplicity, ColorNote is basically a collection of virtual Post-Its. You can from simple note taking or a checklist format. I use this app for my grocery list (it’s easy to check and un-check items as you run out, so you don’t have to retype them) and on the go note taking.